Rotary heat exchanger



May 24, 1966 G. .1. HUEBNER, JR

ROTARY HEAT EXCHANGER 5 Sheets-Sheet 1 Filed July 20, 1965 Geo rye J."

y ,1966 G. J. HUEBNER, JR 3,252,506

ROTARY HEAT EXCHANGER Filed July 20, 1965 j 5 Sheets-Sheet 2 INVENTOR- Geo age J. Hue-22:22; J9:

BYA/T May 24, 1966 e. .1. HUEBNER, JR 3,252,506

ROTARY HEAT EXCHANGER Filed July 20, 1965 5 Sheets-Sheet 5 IN V EN TOR.

E;- T Mwlwm y 1966 G. J. HUEBNER, JR 3,252,506

ROTARY HEAT EXCHANGER Filed July 20, 1965 5 Sheets-Sheet 5 United States Patent 3,252,556 ROTARY HEAT EXCHANGER George I. Huehner, Jr., Bloomfield Hills, Mich, assignor to Chrysler Corporation, Highland Park, Mich., a corporation of Delaware t Filed Huly 20, 1965, Ser. No. 473,475 13 Claims. (Cl. 165-10) minimizing resistance to gas flow through the regenerator matrix while at the same time achieving rapid and efiicient heat transfer from the hot exhaust gases to the cooler high pressure inlet air from the compressor.

According to one embodiment of the invention asset forth in the following specification, a rotary heat exchanger having a generally'cylindrical form is provided with a hub upon which is formed a matrix structure having smooth straight axially extending passages therethrough. A peripheral rim member is mounted upon the matrix structure in concentric relationship with respect to the hub. The assembly is mounted transversely with respect to the air discharged from an intake compressor unit and with respect to the exhaust passageways of a gas turbine powerplant. The axial passages through the matrix structure are adapted to conduct the compressed intake air and exhaust gases therethrough at angularly spaced positions. The exhaust gases are effective to heat the proximate matrix structure to a temperature which approaches in magnitude the temperature of the powerplant exhaust gases. Upon rotation of the regenerator about its axis, the heated portion of the regenerator matrix is brought into contact with the cooler compressed intake air as the same passes through the heated air passages, thereby heating the compressed gas turbine intake air which is then conducted to the burner.

One of the several objects of the present invention is to provide a rotary regenerator unit which will be capable of establishing a temperature gradient across the length of the gas passages therein. The temperature gradient is highly desirable because it makes possible a greater increase in the temperature of the intake air.

Another object of the present invention is to provide a rotary regenerator unit for use with a gas turbine powerplant or the like which is relatively light in weight and inexpensive to manufacture and which achieves optimum heat transfer efficiency with minimum size and weight.

Although the counterflow type regenerator itself is not new, such a regenerator wherein comparatively cool inlet air flows in one direction through parallel gas passages of the matrix, followed by flow of the hot exhaust gases in the opposite direction through the same passages, gives rise to particular problems in the attainment of efficient operation which are not encountered in other type of heat exchangers. An important aspect of the present invention has been the discovery that a particular relationship between the thickness of the walls of the individual gas passages and the shape and hydraulic diameter of these passages results in a regenerator of optimum heat transfer efficiency with minimum size and weight. In particular, it has been discovered that the reduction in thickness of the individual gas passage walls goes handin-hand with an appreciable elongated cross sectional shape in order to obtain optimum heat transfer.

In order to concisely set forth the structural char-acteristics and mode of operation of the present invention, reference will be made to the accompanying drawings in which:

FIGURE 1 is a schematic representation of an automobile gas turbine powerplant showing the relative position of the various components thereof including the rotary regenerator of the present invention;

FIGURE 2 is an end view of the assembly of FIG- URE 3;

FIGURE 3 is a complete assembly view of an actual operative gas turbine powerplant showing the rotary heat exchanger of the present invention incorporated therein;

FIGURE 4 is a view taken along section line 44 of FIGURE -3 showing the segmental inlet and outlet portions for conducting air through the regenerator in either axial direction;

FIGURE 5 is a perspective view partly in section showing the rotary regenerator unit of the present invention isolated from the assembly of FIGURE 3;

FIGURE 7 is an enlarged schematic cross sectional 7 view showing the heat flow associated with a single gas flow passage;

FIGURE 8 illustrates the relationship between Nusselts number N and a function =K T/KfD for various regenerator flow passages of the type illustrated in FIG- URE 7; and

FIGURE 9 illustrates the relationship between Nusselts number and the wall thickness of various stainless steel regenerator flow passages of the type illustrated in FIGURE 7.

For a more complete description, reference will be made first to the schematic representation of a gas turbine powerplant in FIGURE 1 wherein numeral 10 is used to designate the gas turbine compressor with an inlet at 11 and a high pressure discharge passage at 12. The passage 12 conducts intake air to the rotary regenerator 13 which in turn allows the intake air to pass axially therethrough into passage 14 and the burner 15. Upon reaching the burner, the intake air is mixed with fuel and then burned. The burned gases pass through passage 17 to the turbine 18 which in turn drives the compressor shaft 19 and the power output shaft 20. The hot turbine exhaust gases are then conducted through passage 21 and the regenerator 13 to the exhaust port 22. The exhaust gases cause a portion of the regenerator to become heated while passing therethrough. A suitable driving means 23 is provided to rotate the regenerator about its own axis which causes the portion of the regenerator unit which is heated by the exhaust gases to come in contact with the intake air passing from passages 12 to 14 thus heating the same to a temperature which approaches in value the temperature of the exhaust gases.

Having thus described the general arrangement of the component elements of the powerplant, reference will now be made to the operative powerplant assembly as shown in FIGURE 3 which incorporates the regenerator unit of the present invention. The compressor unit, shown generally at Ill, comprises a converging inlet 11 which is open to the surrounding atmosphere throughout its entire periphery. A rotor member 24 of the compressor is effective to force the intake air from the inlet portion 11 into an annular diffuser member 29 where a suitable intake air pressure head is created. The rotor member 24- comprises suitable vanes 25 disposed. about the hub 28 of the rotor for forcibly feeding the intake air to the diffuser 29 and also a radially extending portion at having a peripheral discharge opening 30 for creating a centrifugal head. The ditfuser 29 blends into a wide mouthed portion, shown at 31, as it progresses circumferentially about the axis of the powerplant. The portion 31 covers a segmental portion of the regenerator unit shown at 13. This segmental portion is shown at X in FIGURE 4. A graphite sector plate or seal 32 is provided for sealing the inlet portion 31. Smooth contact surfaces 32' and 32" are provided on seal 32 for engaging the rotating surface of the regenerator unit 13 and the diffuser portion 31 respectively. An additional sealing means may be provided at 33 to insure a sealing contact between portions 31 and the stationary graphite seal 32. Another graphite sector plate or seal 35 is provided on the opposite side of the regenerator unit and is shaped similar to seal 32. Both of the seals 32 and 35 have segmental openings to allow the portion X of the regenerator unit to 'be exposed The passage 14, which was referred to previously in connection with the schematic drawing of FIGURE 1, is shown in FIGURE 3 in close proximity to the regenerator unit 13 and is adapted to conduct the intake air passing through the regenerator from diffuser portion 31 to the burner 15. After the fuel is mixed with the intake air and burned, the burned gases pass into the passage 36 and then into the exhaust chamber 42. While passing from passage 36 to chamber 42 the burned gases pass through an annular channel 37 in which are disposed annular cascades of turbine blades 38 and 39 and associated stator blades 40 and 41. The burner 15 is illustrated by means of an outer elevation view in FIGURE 2. The actual path followed by the intake air and combustion gases through the burner will not be described in detail since the burner does not form a part of this invention.

The blades 38 are mounted upon a primary turbine member 43 which is mounted upon an axially extending shaft assembly 44 which in turn is drivably secured to the compressor rotor hub 28.

The blades 39 are mounted upon a secondary turbine member 45 which is mounted upon an axially extending shaft 46. The shaft 46 is drivably connected to the input pinion gear of a reduction gear transmission assembly which is designated generally by numeral 47. A power absorbing means may be connected to the transmission power output tailshaft 48.

The exhaust chamber 42 is formed to cover a large'segmental portion of the regenerator unit 13 which is shown at Y in FIGURE 4. The graphite seals 32 and 35 are also provided with mating segmental openings to cause the portion Y of the regenerator to be exposed to the exhaust gases. A suitable housing 50 is adapted to form a passageway 51 to conduct the exhaust gases passing through the segmental portion Y of the regenerator to an exhaust port.

It should be noted from FIGURE 3 that the seals 32 and 35 are effective to seal the exhaust gases passing from chamber 42 to passageway 51 as well as to seal the intake air passing from portion 31 to passageway 14 so that the exhaust gas and intake air are not intermixed.

The total area provided at Y for the passage of exhaust gases through the regenerator unit is larger than the area at X for the intake air because the volume occupied by the heated exhaust gas is necessarily larger. It has been found that a ratio of approximately two to one between the exhaust and intake areas is adequate for the usual operating temperatures encountered.

The regenerator unit 13, which comprises the subject matter of the present invention, is shown more in detail in FIGURES and 6. The unit itself comprises a hub 52 and a rim portion 53 which may be made of any suitable material, such as steel. The hub has a suitable bearing means 54, for rotatably mounting the regenerator unit upon a shaft 55, which is mounted in the outer housing. The rim portion is provided with a peripheral ring gear 56 which serves as a means for driving the regenerator unit about its own axis on bearing means 54. Any suitable power source may be used to drivably engage the ring gear 56.

The body of the regenerator unit 13 comprises a rigid metal matrix structure which is formed upon the hub 52 and secured thereon by means of the concentric rim portion 53. The material of the matrix is smooth surfaced, capable of withstanding the cylic temperature extremes to which the regenerator is subject during operation, and has a comparatively high coefficient .of specific heat and comparatively low coeflicients of thermal conductivity and expansion. A satisfactory matrix structure as shown in FIGURES 5 and 6 may comprise a thin metallic strip or ribbon 60 of an iron based alloy such as a mild steel, coated with aluminum or chromium to reduce oxidation or having outer surfaces of iron alloy of aluminum and/ or chromium, or a stainless steel, for example, having a thickness of approximately .001 inch. This thickness will vary as described below in accordance with FIG- URE 8 depending on the thermal and strength properties of the specific material. Iron based alloys are preferred for reasons of economy, but the concept of the present invention also applies to other suitable metals or alloys, as will be apparent below.

A series of transverse ribs 61 are formed on the strip 60 at spaced intervals of .approximately .15 inch. It is desirable to form the ribs with a height of approximately .01 inch. The strip 60 is wound spirally about the hub 52 so that the ribs are effective to maintain a clearance between the layers as shown in FIGURE 6. The layers are fused together by brazing or other means along the outer edges of the ribs 61.

The axial thickness of the matrix will be varied according to the design requirements. A thickness of approximately three inches is adequate and enables the desired laminar flow through the matrix when the unit is used with a gas turbine powerplant having a rated power of about horsepower.

For the purpose of particularly pointing out the mode of operation and the effectiveness of the present invention, the path of gas flow through the gas turbine powerplant will be followed together with a reference to some typical operating temperatures for a 150 horsepower powerplant. The path of the gas flow is illustrated by arrows in FIGURE 3.

Standard atmospheric conditions are assumed at the intake portion of the compressor 10. When the intake air passes through the rotor and is compressed, the temperature increases to approximately 400 F. The temperature of the intake air is therefore approximately 400 F. at the time it enters the inlet segmental portion X of the regenerator unit 13. While passing through the regenerator from chamber 31 to passage 14, the intake air temperature is increased to about 900 F. The passageway 14 conducts the heated intake air to the burner 15 where the combustion process causes the temperature to increase to about 1500 F. The products of combustion are conducted through passage 36 to the turbine members. The work performed on the turbine member is accompanied by a temperature drop to approximately 1000 F. The heated exhaust gases then pass from chamber 42 through the segmental portion Y of the heat exchanger unit and heat the matrix. This is accompanied by a temperature drop in the exhaust gases to approximately 500 F. The passageway 51 then conducts the cooled exhaust gas out a suitable exhaust port.

It should be observed that the hot exhaust gases pass from one side of the heat exchanger to the other in an axial direction. Accordingly, because of the low thermal conductivity of the matrix, a temperature gradient will become established across the axial thickness of the unit with the higher temperature existing at the gas inlet side which is closest to chamber 42 and the lower temperature existing at the gas outlet side. The regenerator unit is constantly rotated during the operation of the powerplant. Accordingly, the hotter part of the matrix will be in contact with the intake air outlet side when rotated so as the intersect the intake air stream. The cooler part of the matrix will, of course, come into contact with the intake air inlet side. Because of the temperature gradient, it is possible to heat the intake air to a higher value than that which would result if such a gradient did not exist, since the intake air comes in contact with portions of the matrix which are heated to a temperature considerably greater than the mean temperature. Since the overall thermal efficiency of the engine is directly dependent upon the temperature of the intake air, it is possible to obtain a higher overall efficiency for the entire unit by making use of the regenerator unit of the present invention.

Prior to the present invention, little was known to the art regarding the heat transfer properties of a multitude of small parallel gas passages having thin walls of the character and dimensions disclosed herein. In order to facilitate understanding of some of the problems involved, an enlarged cross sectional view of a single gas passage 62 is illustrated in FIGURE 7 wherein two of the heat flow components are indicated by arrows A and B.

Hot exhaust gas flowing through passage 62 in a direction perpendicular to the plane of the paper will transfer heat to the inner side walls as indicated by the arrows A. It has long been recognized that the thinner the walls 60 and 61, the greater will be the surface area for any given weight of material and, as far as this factor is concerned, the greater will be the total heat transfer from the gas to the passage walls in a given time limit.

In order to take advantage of the thin-walled effect the obvious step was to employ a fibrous matrix, as for example glass or metal fibers for the heat exchange medium. Such constructions have been unsuitable for use with automotive gas turbine engines wherein the gas flow is at comparatively high velocity and pressure. Not only do particles of the fibrous material break off when sub ject to the high pressure and cyclic temperature changes and damage the extremely high speed turbine blades, but the resistance to. gas flow is prohibitive in a regenerator having random gas flow passages.

Accordingly, the present invention utilizes a multitude of preformed flow passages having thin film-like smooth walls extending directly through the regenerator in axial side-by-side relationship and sealed along their axial length to prevent circumferential flow of gases from one gas passage to another within the regenerator matrix. The use of the smooth axial flow passages enables an increase in the total surface area to an optimum value for any given weight of regenerator without unduly increasing the flow resistance. It will also be assumed herein that the compressor 10 and regenerator matrix are designed to effect laminar flow of gases through each passage 62, as distinguished from turbulent flow, for the sake of minimizing the resistance to the gas flow. In addition, as described more fully below, the dimensions specified achieve optimum thermal efficiency by providing answers to problems that were not known to exist heretofore.

Referring to FIGURE 7, during the operating cycle when a gas passage 62 is being heated by the gas passing therethrough, it-has been found that the transfer of heat from the gas to the passage walls of elongated cross sectional area is substantially less adjacent the small edges a than at the mid-region of the long dimension b of the passage. Thus, each flow passage 62 adjacent its small edges a will be relatively cooler than said mid-region. In consequence, the portions of each gas passage 62 adjacent its opposite small edges a will be relatively ineffective as a heat transfer medium unless the heat flow indicated by the arrows B within the material of the walls can be used to conduct heat within the passage side walls toward the small edges a. A similar problem arises during heat transfer from the passage sidewalls to the gas.

It is therefore to be realized that a definite but heretofore unexpected relationship exists between cross sectional elongation and wall thickness. The less the elongation and the greater the number of total gas passages,

the greater will be the total efiiect of the small edges a in reducing the heat transfer efliciency of the regenerator. Where the walls are reduced to a film-like thickness, as in the present invention, the cross sectional elongation must be increased substantially, otherwise the loss in heat transfer efficiency resulting from reduced heat transfer toward the small edges of each passage becomes a significant consideration.

On the other hand, the thinner the passage walls, the greater will be the resistance to heat flow therein toward the small edges a and the greater will be the loss in heat transfer eificieucy. This latter concept is directly opposed to the practice heretofore of attempting to increase the total surface area and heat transfer efficiency by decreasing the wall thickness of the individual gas passages. As explained below the gas passage walls cannot be reduced in thickness below a predeterminedminimum without sacrificing optimum heat transfer efficiency.

As the heat flow in the direction of the arrows B increases,- FIGURE 7, the effective utilization of the small end regions of the elongated gas flow passages and correspondingly the heat transfer efficiency of the regenerator will be increased. Likewise, as the elongation of the cross sectional area of each gas passage is increased, the total effect of the small edge portions a of allthe passages tending to reduce the regenerator heat transfer efiiciency will be decreased.

If we assume side walls 60 of infinite thickness so as to minimize resistance to heat flow in consequence of the wall thickness factor, a modulus of heat transfer effectiveness well known as Nusselts number can be correlated directly with the heatlflow within the walls of the gas passages in the direction of the arrows B. For a gas flow passage of square cross section, Nusselts number equals 3.6.

For an elongated gas passage having side walls in the ratio to 12 as specified by applicant, Nusselts number increases to slightly less than 7. Thereafter as the elongation increases to infinity (parallel side walls with no small end walls) Nusselts number increases toapproximately 8.2. The ratio of the dimensions b/a=G is hereinafter referred to as the aspect ratio. Thus as the elongation or aspect ratio G increases froma square or 1:1 ratio to 150:12 ratio, Nusselts number rapidly doubles in value. As the elongation is increased infinitely, Nusselts number asymptotically approaches 8.2. The ratio 150:12 is accordingly within a critical range in that it is at the region of optimum Nusselts number for any practical obtainable increase in the elongation or aspect ratio G. Below the optimum aspect ratio, Nusselts number decreases rapidly. Above the optimum aspect ratio, any advantage obtained from an increase in Nusselts number is negligible whereas the feasibility of increasing the aspect ratio rapidly decreases because of the lack of rigidity of the thin walls which cannot be maintained in parallel spaced relationship over extended distances without intermediate support.

Referring to FIGURE 8, Nusselts number N =HD/ K; is plotted against a dimensionless parameter In the above expressions:

H is the coeflicient of thermal conductance between the walls of the gas passage 62 and the gas flowing therein and measures thequantity of heat flow between the gas and a unit area of the sidewalls per unit time and temperature differential.

D is the hydraulic diameter of the elongated passage 62 and equals four times the flow area divided by the perimeter, which for a rectangle is Zab/ (a-l-b).

T is the thickness of the sidewalls, particularly the sidewalls b, the thickness of the walls a being unimportant when the aspect ratio G=b/a is large. Both T and D are linear measurements, expressed for example in feet (fL).

K and K are the coeflicients of thermal conductivity of the sidewalls and gaseous fluid medium respectively and measure the quantity of heat flow per unit time and temperature ditferential along a unit distance within the sidewalls and gaseous medium respectively. Inasmuch as the combustion products of an automotive gas turbine engine comprise a comparatively small portion of the total mass of the inlet air, the difference in the values of K for the inlet air and exhaust gas is negligible. Hence the value of K for air is feasibly employed herein.

It is apparent that Nusselts number N is also dimensionless because, employing conventional units, H/K can be expressed as (Btu/hr. ft. F.)/(B.t.u./hr. ft. F.)=l/ ft. N= (H/K )D=(l/ft.)ft., is therefor dimensionless. The family of curves in FIGURE 8 accordingly represents the relationships between two dimensionless parameters at various aspect ratios and are entirely independent of the material employed for the walls of the gas passage 62 and the fluid flowing therethrough. Regardless of the composition of the fluid medium or the material of the regenerator matrix, there is a definite value of N for each value of and G.

For a regenerator of any given size, the total heat transfer area of the matrix will be increased by increasing the number of gas passages 62. Thus the hydraulic diameter D of each passage 62 will be as small as practicable in order to obtain the maximum number of gas passages 62, the smallness of the hydraulic diameter being limited by the total axial pressure drop across the regenerator that can be tolerated and the volume of gas that can be accommodated by laminar flow. Inasmuch as N=HD/K as N increases in value, the conductance H and corresponding the efficiency of the regenerator increases for any predetermined value of D. Similarly, and correspondingly the weight of the regenerator will increase in value with increasing wall thickness T by reason of the expression =K T/K D.

It is apparent from FIGURE 8 that Nusselts number N increases rapidly as the aspect ratio G increases to the practicable limits 10 or 12, as explained above, but decreases rapidly with decreasing 5 at values smaller than approximately 10, which latter value defines the knee or approximate midpoint of the sharp bend of each curve. For larger values of the thickness T of the passage sidewalls can be increased infinitely without appreciably enhancing the value of Nusselts number N.

On the other hand, as indicated by the two vertical 10% measurements associated with G=l and G=l2 respectively in FIGURE 8, 90% of the theoretical maximum value of Nusselts number N is obtained on the G=10 curve if 4; is approximately 4, and is obtained on the G=l2 curve if is approximately 5. The optimum value of for minimum regenerator mass and maximum heat transfer effectiveness as measured by Nusselts number N is therefore approximately 10 (log =l), but values of as low as'4 (log =.6) will achieve more than 90% of the value of Nusselts number if the aspect ratio G is greater than 10; and similar values of N are obtained when log 5 is 1.4 and G is 6. The two vertical measurements indicate the range of within the upper 10% of the maximum theoretical values of N associated with the curves G=10 and 6:12 respectively. N decreases very rapidly as G decreases toward 4. The lower practical limit for G from a thermo-dynamic standpoint is thus somewhere between 4 and 6 and may be stated as being on the order of about 5.

Specific values of gas passage wall thickness for stainless steel having a comparatively high specific heat and low coefiicient of thermal conductivity, where G=10 and K /K =.002, are illustrated for various hydraulic diameters in FIGURE 9 to emphasize the sharp drop in heat transfer effectiveness when the wall thickness is decreased below the critical value. The uppermost curve D=.025" corresponds approximately to the hydraulic diameter of .the gas passage 62 in FIGURE 7, wherein the wall thickness of the stainless steel gas passages ranges between approximately .0002 and .001 inch for values of log d: between approximately l i.4. The wall thickness of the passages 62 where equals approximately 10 is .0005 inch. Thus a stainless steel matrix having gas passages dimensioned as in FIGURE 7 but with walls 60 approximately .001" thick would combine optimum heat transfer effectiveness with minimum weight near the upper limit of wall thickness as determined by the thermo-dynamic considerations. Thicker gas passage walls would merely increase the mass of the regenerator without materially increasing heat transfer effectiveness. The optimum wall thickness for other suitable matrix materials having the desired high specific heat and low coefficients of thermal conductivity and expansion will similarly be determined by the value of 5 in the critical range log =1.:.4.

The hydraulic diameter D=.022 illustrated in FIG- URE 7 is within a desirable range for an iron alloy regenerator matrix, although hydraulic diameters approximately twice that value have been used satisfactorily. As is apparent from FIGURES 8 and 9, an hydraulic diameter greater than .05 inch would not be practical for a metal matrix having a coefficient of thermal conductivity comparable to stainless steel because too great a wall thickness would be required to maintain 11: approximately equal to 10. Accordingly, with the iron alloy matrix, the lower values of hydraulic diameter D below .05 inch and preferably between .02 inch and .04 inch are preferred.

I claim:

1. A counterflow type regenerator matrix for an automotive gas turbine engine wherein high temperature exhaust gases and cooler inlet gases are alternately directed through portions of said matrix in opposite directions by substantially laminar flow, said matrix comprising a comparatively rigid metallic body having a multitude of substantially parallel gas passages of elongated cross sectional area capable of withstanding the temperatures and pressures of said gases, the walls of longer cross section of each gas passage being substantially parallel to each other and sufficiently smooth and impervious to said gases to effect said laminar flow and being at least several times longer than the smaller cross sectional dimension of said passage, the hydraulic diameter of each gas passage being not greater than a value on the order of about .05", and log K T/K D being between values on the order of about .6 and 1.4, wherein K; is the coefficient of thermal conductivity of the gas flowing through said gas passages, K is the coefiicient of thermal conductivity and T is the thickness of said walls of longer cross section, and D is the hydraulic diameter of said passages.

2. A matrix according to claim 1 wherein the spacing between said walls of longer cross section is on the order of about .01".

3. A matrix according to claim 1 wherein the ratio of the long dimension to the short dimension of the cross section of each gas passage is not less than a value on the order of about 5.

4. A matrix according to claim 3 wherein the hydraulic diameter of each gas passage is on the order of about .02".

5. A matrix according to claim 4 wherein the material of said body is stainless steel.

6. A matrix according to claim 1 wherein the ratio of the long dimension to the short dimension of the cross section of each gas passage is not less than a value ranging on the order of from about 10 to 6 while log K T/K D ranges correspondingly on the order of from about .6 to 1.4.

7. A matrix according to claim 6 wherein the hydraulic diameter of each gas passage is on the order of about .02".

8. A counterflow type regenerator matrix for an automotive gas turbine engine wherein high temperature exhaust gases and relatively cooler inlet gases are alternately directed through portions of said matrix in opposite directions by substantially laminar flow, said matrix comprising a comparatively rigid metallic body of material having a comparatively high coefiicient of specific heat and a comparatively low coefiicient of thermal conductivity and being formed with a multitude of substantially parallel gas passages of elongated cross sectional area capable of withstanding the temperatures and pressures of said gases, the walls of longer cross section of each gas passage being substantially parallel to each other and sufficiently smooth and impervious to said gases to effect said laminar flow and being at least several times longer than the smaller cross sectional dimension of said passage, the hydraulic diameter of each gas passage being not greater than a value on the order of about .05", and log K T/K D being on the order of about 1, wherein K: is the coeflicient of thermal conductivity of the gas flowing through said gas passages, K is the coefficient of the thermal conductivity and T is the thickness of said walls of longer cross section, and D is the hydraulic diameter of said passages.

9. A matrix according to claim 8 wherein the ratio of the long dimension to the short dimension of the cross section of each gas passage is not less than a value on the order of about 5.

10. A matrix according to claim 9 wherein the spacing between said walls of longer cross sect-ion is on the order of about .01".

11. A matrix according to claim 10 wherein the material of said body is an iron based alloy.

12. A matrix according to claim 8 wherein the hydraulic diameter of each gas passage is on the order of about .02".

13. In combination, a counterfiow type regenerator of an automotive gas turbine engine for transferring thermal energy from a stream of heated exhaust gases to a generally oppositely directed stream of relatively cooler inlet gases, compressor means for subjecting said inlet gases to pressure upstream of said regenerator to effect the flow of said streams of gases, said regenerator comprising a comparatively rigid matrix of an iron based alloy having a multitude of substantially parallel gas passages of elongated cross section adapted for substantially laminar flow of said streams of gases therethrough and capable of withstanding the temperatures and pressures of said gases, the walls of longer cross section for each gas passage being substantially parallel to each other and sufficiently smooth and impervious to said gases to efiect said laminar flow, the ratio of the long dimension to the short dimension of the cross section of each gas passage being not less than a value on the order of about 5, the hydraulic diameter of each gas passage being not greater than a value on the order of about .05, means for conducting the two oppositely directed streams of gases alternately to a portion of said matrix for said laminar flow therethrough, and log -K T/K D being between values on the order of about 0.6 and 1.4 wherein K and K are the coeflicients of thermal conductivity of said walls of longer cross section and the gas flowing through said passages respectively, T is the thickness of said walls of longer cross section, and D is the hydraulic diameter of each gas passage.

References Cited by the Examiner UNITED STATES PATENTS 2,023,965 12/1935 Lysholm -1 2,552,937 5/1951 Cohen 165-10 2,596,642 5/1952 Boestad 165-166 2,706,109 4/1955 Odman 165-1O ROBERT A. OLEARY, Primary Examiner.

A. W. DAVIS, Assistant Examiner. 

1. A COUNTERFLOW TYPE REGENERATOR MATRIX FOR AN AUTOMOTIVE GAS TURBINE ENGINE WHEREIN HIGH TEMPERATURE EXHAUST GASES AND COOLER INLET GASES ARE ALTERNATELY DIRECTED THROUGH PORTIONS OF SAID MATRIX IN OPPOSITE DIRECTIONS BY SUBSTANTIALLY LAMINAR FLOW, SAID MATRIX COMPRISING A COMPARATIVELY RIGID METALLIC BODY HAVING A MULTITUDE OF SUBSTANTIALLY PARALLEL GAS PASSAGES OF ELONGATGED CROSS SECTIONAL AREA OF CAPABLE OF WITHSTANDING THE TEMPERATURES AND PRESSURES OF SAID GASES, THE WALLS OF LONGER CROSS SECTION OF EACH GAS PASSAGE BEING SUBSTANTIALLY PARALLEL TO EACH OTHER AND SUFFICIENTLY SMOOTH AND IMPERVIOUS TO SAID GASES TO EFFECT SAID LAMINAR FLOW AND BEING AT LEAST SEVERAL TIMES LONGER THAN THE SMALLER CROSS SECTIONAL DIMENSION OF SAID PASSAGE, THE HYDRAULIC DIAMETER OF EACH GAS PASSAGE BEING NOT GREATER THAN A VALUE ON THE ORDER OF ABOUT .05", AND LOG10 KWT/KFD BEING BETWEEN VALUES ON THE ORDER OF ABOUT .6 AND 1.4, WHEREIN KF IS THE COEFFICIENT OF 